The differences in inflammatory response to gonococcal strains which cause pelvic inflammatory disease (PID [local inflammatory response]) and disseminated infection (DGI [no local inflammatory response]) has been associated with the ability of the corresponding strains, which have been passed in vitro, to be killed or to resist killing by antibody and complement in normal human serum (NHS). When incubated in NHS, the complement-derived neutrophil chemoattractant C5a is more rapidly generated by serum-sensitive (SS) than by stable serum-resistant (SR) strains. Our preliminary data have implicated lipooligosaccharide (LOS) antigens as causative in serum-sensitivity and -resistance of gonococci. We have also observed increased binding of the hemolytically inactive C3b cleavage product, iC3b, on the surface of SR strains (as compared to SS strains) both in vitro and in vivo. This suggests a mechanism (i.e., less active C5 convertase formation) whereby SR strains generate less C5a and, concomitantly, less local inflammation than SS strains. We have also demonstrated the importance of the protein III (PIII) antigen in the blocking antibody effect, which contributes to serum-resistance, and have defined selected determinants of PIII as specific targets of blocking antibody. The proposed studies will examine the mechanisms underlying these observed differences in order to more clearly understand the pathogenesis of the related clinical inflammatory syndromes. Specific Aim 1 will complete our examination of the forms of C3b and C4b bound by phenotypically different strains and liposome models that reproduce these phenotypes, through use of labelled C3 and C4 and monoclonal antibody (mAb) reagents specific for cleavage fragments (i.e. iC3b). We will examine binding in the absence and presence of specific antibody in order to elucidate the role of antibody in these interactions. Specific Aim 2 will investigate the role of regulation of activation of both pathways of complement. We will specifically examine the relative activity of i) factors B and H in the alternative pathway and ii) C4 binding protein in the classical pathway. Specific Aim 3 will investigate the possibility that certain strains of gonococci express substances capable of inactivating complement components (C3b, C4b, or C5a), either through proteolytic or cofactor activity. We will use well characterized strains, PIII, and LOS mutants, plus antigen sensitized liposome counterparts in our studies. Specific sera (both human and murine monoclonal) of known functional specificity will allow further definition, at the level of antibody and complement, of how different gonococcal surface determinants effect C3b and C4b deposition and cleavage, and diminished C5a activity.